Rename item-subsystem methods (refactor step 5, items)

getItem→promptPackItem now returns (obj, ok) instead of a nil-signaling
pointer; invName→inventoryName; doPot→applyPotionFuse. C breadcrumbs
kept. Behavior unchanged; suite green.

game/potions.go

@@ -16,9 +16,9 @@ type pact struct {
 // quaff drinks a potion from the pack (potions.c quaff).
 func (g *RogueGame) quaff() {
 	p := &g.Player
-	obj := g.getItem("quaff", KindPotion)
+	obj, ok := g.promptPackItem("quaff", KindPotion)
 	// Make certain that it is something that we want to drink
-	if obj == nil {
+	if !ok {
 		return
 	}
 
@@ -43,7 +43,7 @@ func (g *RogueGame) quaff() {
 
 	switch obj.PotionKind() {
 	case PotionConfusion:
-		g.doPot(PotionConfusion, !trip)
+		g.applyPotionFuse(PotionConfusion, !trip)
 	case PotionPoison:
 		g.Items.Potions[PotionPoison].Know = true
 		if p.IsWearing(RingSustainStrength) {
@@ -118,11 +118,11 @@ func (g *RogueGame) quaff() {
 			g.SeenStairs = g.seenStairs()
 		}
 
-		g.doPot(PotionLSD, true)
+		g.applyPotionFuse(PotionLSD, true)
 	case PotionSeeInvisible:
 		show := p.On(CanSeeInvisible)
 
-		g.doPot(PotionSeeInvisible, false)
+		g.applyPotionFuse(PotionSeeInvisible, false)
 
 		if !show {
 			g.invisOn()
@@ -177,9 +177,9 @@ func (g *RogueGame) quaff() {
 
 		g.msg("hey, this tastes great.  It make you feel warm all over")
 	case PotionBlindness:
-		g.doPot(PotionBlindness, true)
+		g.applyPotionFuse(PotionBlindness, true)
 	case PotionLevitation:
-		g.doPot(PotionLevitation, true)
+		g.applyPotionFuse(PotionLevitation, true)
 	}
 
 	g.status()
@@ -194,9 +194,9 @@ func (g *RogueGame) raiseLevel() {
 	g.checkLevel()
 }
 
-// doPot does a potion with standard setup: it uses a fuse and turns on a
-// flag (potions.c do_pot).
-func (g *RogueGame) doPot(kind PotionKind, knowit bool) {
+// applyPotionFuse does a potion with standard setup: it uses a fuse and
+// turns on a flag (potions.c do_pot).
+func (g *RogueGame) applyPotionFuse(kind PotionKind, knowit bool) {
 	pp := &g.data.pActions[kind]
 	if !g.Items.Potions[kind].Know {
 		g.Items.Potions[kind].Know = knowit